As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine such as a milling or boring machine to securely hold a cutting tool upon the machine during the cutting of a work piece. In most prior art tool holders, a central aperture is formed therein for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine. Subsequent to the insertion of the shank portion of the cutting tool into the central aperture, the tool holder is drawn or pulled tightly into the spindle so as to rigidly maintain the cutting tool within the tool holder.
In certain machining applications, it is necessary to use what is commonly referred to as a "long reach" cutting tool which comprises an elongate, extended shank portion having a cutting head disposed on one end thereof. The end of the shank portion opposite that including the cutting head is inserted into the central aperture and rigidly maintained within the tool holder when the tool holder is drawn into the spindle of the milling or other machine. As is well known, cutting tools, including those of the long reach variety, are typically fabricated from tungsten carbide due to its extremely high level of hardness. However, though being extremely hard, tungsten carbide is also brittle. In this respect, when a long reach cutting tool is used in high speed and other milling applications and an excessive amount of shear force is applied to the cutting head thereof, there is a tendency for the shank portion of the cutting tool to fracture in view of the brittleness of the tungsten carbide material used to fabricate the cutting tool. As will be recognized, such catastrophic failure of the cutting tool poses the threat of causing serious injury to the machine operator.
Additionally, a significant deficiency associated with the prior art tool holders themselves is that the manner in which the shank portion of the cutting tool is secured within the central aperture of the tool holder often results in the non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is extremely undesirable, particularly in modern, high tolerance machining applications such as those performed on a vertical milling machine wherein minor variations in the concentricity of the cutting tool within the tool holder often times results in extreme flaws in the cutting operation.
The present invention addresses the deficiencies of prior art long reach cutting tools and tool holders by providing a machine tool extension which is adapted to interface a tungsten carbide cutting tool to a tool holder and is significantly less susceptible to fracture. The extension of the present invention is also constructed to substantially eliminate the non-concentric mounting of the cutting tool relative to the tool holder by facilitating the interface of the cutting tool to the tool holder through the use of heat shrink fitting techniques.